Influence of Phosphorus Application with Avail on Following Soybeans in Southeastern Coastal Plains

Application of Phosphorus (P) in combination of with polymer Avail to previous crop may affect soybeans [Glycine max (L.) Merr.] under dryland conditions. The objective of this study was to determine the effect of two P rates (45 and 90 kg P₂O₅ ha^-1) with and without Avail applied to winter wheat (Triticum aestivum L.) previous crop on growth and yields of dryland soybeans near Blackville, SC from 2011 to 2012. Soybeans were evaluated for Leaf Area Index (LAI), plant Normalized Difference Vegetation Index (NDVI), plant height, grain moisture, seed weight and grain yields. Compared to untreated control, P applications at 45 kg and 90 kg ha^-1 with Avail to winter wheat significantly increased soybean grain yields by 12.3% and 20.2%, respectively. Phosphorus applied to previous crop at 45 kg and 90 kg P ha^-1 with polymer Avail, improved soybean yields by 8.1 and 4.0% over P treatments not treated with Avail, respectively. Soybean LAI significantly increased by 22.8% at 3 months after planting with application of P at 90 kg ha^-1 and polymer Avail to winter wheat previous crop compared to untreated control. Lower P rate of 45 kg ha^-1 with Avail to winter wheat increased soybean LAI by 11.8%. Applications of 45 kg and 90 kg P ha^-1 with Avail to previous crop improved plant NDVI at 3 months after soybean planting by 1.8% and 2.5%, respectively. Based on significant linear relationship, increasing plant NDVI by 0.1 improved soybean yields by 126.1 kg ha^-1. Applications of P with Avail to winter wheat did not affect soybean LAI and NDVI at 2 months after planting, plant height, grain moisture and seed weight. Results from this study indicate that P applications with Avail to previous crop significantly improved plant LAI and NDVI at 3 months after planting and increased soybean yields.